"Core-Shell" Diamond Nanoparticles with NV- Centers and a Highly Isotopically Enriched C-13 Shell as a Promising Hyperpolarization Agent

In this article, we demonstrate the synthesis of "core-shell" diamond nanoparticles, possessing nitrogen-vacancy (NV-) centers and naturally abundant C-13 in the inner part (or the "core") and a highly isotopically enriched outer part (or the "shell"). Such nanoparticles are formed by overgrowth over previously electron-irradiated nanodiamonds under high-pressure high-temperature conditions. The synthesized diamond material is investigated using microscopy and spectroscopy techniques. Raman spectroscopy provides an estimate (96%) for the C-13 isotopic content within the "shell", and the persistence of NV-centers in the natural abundance "core", providing an optically detected magnetic resonance signal, is confirmed. Considering the measured nuclear polarization lifetime (T-1 similar to 90 s), the estimation of the spin diffusion length for the "shell" nuclear spins reveals that C-13 can act as a vector for transferring the spin polarization from NV- centers to the surface. These particles, therefore, offer a promising platform for the hyperpolarization of nuclear spins in a fluid.